1. Field of the Invention
The invention relates to a vehicular ejector system and a control method thereof. More particularly, the invention relates to a vehicular ejector system capable of causing an ejector to function suitably and cost efficiently during idling.
2. Description of the Related Art
In vehicles, an ejector has been used to supply a negative pressure chamber of a brake booster with a negative pressure that is greater than the negative pressure (hereinafter, also referred to simply as “the negative pressure in the intake system”) that is to be extracted from an intake passageway of an intake system of an internal combustion engine (hereinafter, also referred to simply as “the intake system of the internal combustion engine”) that connects in communication from the atmosphere to the cylinders of the engine. Generally, the ejector is disposed in a bypass that bypasses the throttle valve, and generates great negative pressure due to the venturi effect. With regard to the ejector, for example, Japanese Patent Application Publication No. 62-214245 proposes a negative pressure source device of negative pressure booster that employs an ejector. This negative pressure generator device employs a pressure sensor that detects that the negative pressure of the negative pressure chamber has become less than or equal to a predetermined value. Furthermore, Japanese Patent Application Publication No. 2005-69175 proposes a vehicular control device that has correction means for correcting the intake air amount taken into the internal combustion engine on the basis of the state of operation of the ejector.
Generally, the negative pressure in the intake system becomes the greatest at the time of idling. Therefore, the negative pressure in the negative pressure chamber (hereinafter, also referred to simply as “the booster negative pressure”) is secured in a magnitude that is sufficient at the time of idling. When the ejector is not functioning, the brake booster directly extracts the negative pressure from the intake system. The magnitude of the negative pressure in the intake system varies under various conditions while the engine remains in the idling state. That is, in some cases during idling, the negative pressure in the intake system can be small and insufficient in terms of the magnitude of the booster negative pressure. In such a case, the assist force of the brake booster declines, so that the operation burden on the driver increases.
If a pressure sensor that directly detects the booster negative pressure is utilized, the magnitude of the negative pressure in the negative pressure chamber of the brake booster can easily be grasped. Therefore, the provision of such a pressure sensor is favorable in causing the ejector to function so as to supply the brake booster with increased negative pressure when the negative pressure in the intake system is small. It can be said that it suffices to cause the ejector to function when the negative pressure in the intake system is small, in order to secure a sufficient magnitude of the booster negative pressure. However, providing a vehicle with such pressure sensors to cause the ejector to function will naturally result in a corresponding increase in the cost of the vehicle.